This application is an amended version of the application with U.S. Ser. No. 07/892,335 which was filed on Jun. 2, 1992.
1. Field of the Invention
This invention provides means for entry of driver-controlled vehicles into an automatic highway system, for transition of the vehicles to automatic control, for controlling the longitudinal motion of the vehicles on the highway, for protecting the vehicles against collision, and for effecting the transition back to driver control and exit from the highway. The invention employs reference means that are compatible with the reference requirements of an automatic lateral control system. The invention also provides means for interacting cooperatively with the lateral control system through provision of steering inputs needed by vehicles for following highway directional changes and for performing lane-changing operations. Finally, the invention provides means for insuring fail-safe and fail-operational performance.
2. Description of the Prior Art
It has been anticipated for many decades that current highway systems would be upgraded, through developments in technology, to enable complete automatic control of vehicles. A model of such a highway system was a popular feature of the 1939 New York World's Fair. The expected benefits of such a system were relief of the drivers from the strain and effort of controlling their vehicles, increased traffic densities and increased safety resulting from elimination of human error.
The primary technical problems associated with realization of automated highways are achievement of vehicle longitudinal control, through inputs to the braking and propulsion systems, and achievement of vehicle lateral control, through inputs to the steering system. Associated with these fundamental problems are higher-level problems such as lane changing, route control, headway control, collision avoidance and transitions between the operator-controlled state and the automatically controlled state.
Automated highway systems will be subject to unique safety constraints. Vehicles operating in public transportation systems uniformly observe the "brickwall stopping criterion," which insures that vehicle spacing will allow a trailing vehicle to come to a safe stop at an emergency braking rate that will not subject passengers to injury or excessive discomfort, in the event that a leading vehicle makes an infinitely rapid stop (as if hitting a brick wall). Drivers of automobiles, on the other hand, consistently disregard the brickwall stopping criterion. Headways of two seconds or less, at speeds in the neighborhood of 55 mph, are common on highways. Such headway spacings are substantially shorter than the headway requirements of the brickwall stopping criterion. The vehicle capacity attained with an automated highway system must exceed, or at least equal, the vehicle capacity of existing highways, while substantially reducing the risk of collision. An automatic control system for vehicles on highways must permit a range of headways to accommodate road conditions and the headway policy of the operating authority.
Means proposed for automatic longitudinal control of vehicles on highways include microwave or optical radar systems for measurement of intervehicle distances (see, for example, S Shladover et al., "Automatic Vehicle Control Developments in the PATH Program," IEEE Transactions on Vehicular Technology, Vol. 40, No. 1, pp.114-130, Feb. 1991).
Lateral control means adapted to installation in automobiles were developed and tested at Ohio State University in the 70's. The Ohio State development was based on the "wire-follower" concept wherein a current-carrying wire in the surface of the roadway defines the path followed by the vehicle. Equipment on board the vehicle responds to the magnetic field of the current flowing in the wire and makes steering corrections to enable the vehicle to follow the desired path (see, for example, R. E. Fenton, "On the Steering of Automatic Vehicle: Theory and Experiment," IEEE Transactions on Automatic Control, Vol. AC-21, pp.306-315, June 1976). A disadvantage of wire-follower lateral control is a requirement for enclosing the wire in a slot in the roadway, since such modification of the roadway would make the roadway surface vulnerable to erosion from weather.
More recently, vehicle lateral control means have been based on the concept of defining the vehicle reference path by a sequence of magnetic nails driven into the highway. The reference means in this case would be less likely to expose the highway surface to weather damage than wire follower reference means. A group at the Institute of Transportation Studies of the University of California, in a joint venture with a private firm, has developed and demonstrated such a system (see W. Zhang et al, "Full-Scale Experimental Study of Vehicle Lateral Control System," Transportation Research Board Record No. 1358, pp. 36-41, 1992).